[python] Re: Lean Steer Python/Hipparion Trike

  • From: Henry Thomas <whpthomas@xxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Mon, 08 Jan 2007 23:12:26 +1000

George Durbridge wrote:

It is very exacting and hard to get your head around at times.

Agreed - I am still trying to think out a lot of it.
Actually with the new simulation geometry it is making a lot more sense, the funny thing is that only one variable really matters, all the other ones have a marginal impact. I will detail this when I am finished drawing up some diagrams to explain it clearly.

Thanks for those references.  The previous trikes all used a rocker arm
moving in a vertical plane about a horizontal pivot, but your current
design has the rocker arm moving in a horizontal plane about a vertical
pivot: did you make that change to achieve self-centring, or for
construction reasons?
Much like the python pivot, it doesn't mater how height it is off the ground, as long as it pivots on the axis at the correct angle and trail. Likewise with this you can rotate the mechanism around the pivot axis and place it where it is easiest to construct. It did I guess effect the self centering effect in that by separating the leaver from the arm I was able to simulate it better.

Either way, had you thought of substituting a
stiff leaf spring for the rigid rocker arm, to allow some suspension
movement, other than pure roll?
This is a nice idea, but might be a bit heavy. I am looking at placing an elastomer on each end of the rocker arm.

By leaning the wheels, we are loading them with cornering forces they
are designed to resist, unlike trikes cornering with upright wheels.
And, unlike so many leaning trikes, you do it with all three wheels.
While that has to be a good thing, it really affects how long the wheels
will last, rather than the cornering forces we can generate in the
meantime.
I disagree, the thing I didn't do before but have done since, is draw a line collinear with the riders CoG to the ground. It turns out that the line is neutral, just like a bike. It doesn't move out or in as the trike tilts. I was surprised to discover this as I thought it looked like it moved marginally out, but it was just an optical illusion. So if the line doesn't move from center, and the rear wheels are parallel with it, then they behave just like a bike and only have a radial load, not a angular load, so I would not expect them to wear any differently. Even so, I have 48 spoke BMX wheels for the back with double wall rims and 14mm axles just in case ;-)

However, if the CoG neither falls nor moves inward when the trike leans,
have we improved the trike's cornering power at all?  The cornering
force it can generate (if the tyres and everything else are up to it) is
limited by the location of the CoG: the maximum cornering force in g is
equal to the tangent of the angle to the horizontal of the line from the
outer contact patch to the CoG.  Unless we can reduce that angle, can we
improve the cornering?
I think this is where my earlier description might have been confusing. If you imagine a rider on a bike with the contact patch below them, as they lean they move in an arc about the contact patch. My tilting mechanism does just this, except at the same time the rider leans, they are also moving away collinearly from the contact patch, so that their actual height parallel to the ground is lifted ever so slightly. The effect is that the static force of this lifting will tend to self center the trike. However if the rider leans and moves their CoG to one side or the other, this shift in weight will over come the self centering effect. That is it should be easy to find an equilibrium yet easy to lean and tilt.

Of course, all of this assumes you are strapped to the seat, not leaning
further into the corner than the seat: maybe the real point is that the
leaning seat will facilitate your moving the CoG into the corner,
without hindering you straightening up again.

The other thing to know about my design is that the tilt angle is naturally self limiting. That is, it will only tilt 25-30 degrees and lock -- this is an effect of the geometry. The rider CoG never exceeds the inside wheel, so they will never tip over.

In the case of high speed cornering this you will have to lean your body to move your CoG further than the maximum tilt will permit. However if you refer to my banking tables, http://jetrike.com/banking this maximum tilt angle should be fine for commuting and touring speeds.

So as you suggest, I guess if you are already in a lean, it is easier to lean further. Compared to non-tilting trikes you should be able to take corners at higher speeds with a tilting trike. Finally, most roads have a camber that is constant regardless of vehicle weight, so you generally don't have to tilt at high speeds on roads as much as you might think -- provided you live in an area that has properly engineered roads -- you can corner at the posted speed limit without a worry.

-h
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